A method for producing a polyolefin by polymerizing olefins in a system having a plurality of gas-phase polymerization tanks in which olefins are polymerized is conventionally known.
The method is disclosed in Japanese Unexamined Patent Publication No. 2011-508800, Japanese Unexamined Patent Publication No. 2003-277412, U.S. Pat. No. 5,235,009, and Japanese Unexamined Patent Publication No. 2009-173897, etc.